Or, at least, that you're in a duplicate town, house, and hospital. Reduplicative paramnesia victims believe that someone or something has constructed a duplicate structure, that looks exactly like the one they remember being in. What part of the brain can make you think you're on the set of your own life?

One day, a 71-year-old man went missing after he left a friend's party. His family at first thought that his bus home was late. After some time, they became alarmed and wondered how to find him. Fortunately for them, about five hours after he was initially expected back, he came home in a taxi. His daughter, concerned for him, ran out to the taxi to see how he was and ask why he was missing for so long. He recognized her and seemed perfectly fine, but had a question for her. What was she doing "in this place." When asked why she wouldn't be there, he told her that this was not his house, but an identical duplicate house. He was immediately admitted to the hospital.

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Another man was already in the hospital, after a head injury. He spoke perfectly well with his friends, family, and hospital personnel, but insisted that he was in a duplicate hospital. A woman with the same delusion was asked whether the other hospital had different doctors and staff working there. She said no. The doctors in her hospital also worked at the other hospital.

All these people have reduplicative paramnesia – which most doctors think is a fancy way of saying a lesion in the frontal lobe of their brain. Doctors first suspected a physical cause to this seemingly psychological delusion when they noticed that it was (relatively) often found in soldiers, or people who had hurt themselves.

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The most common characteristic of this condition is the conviction — in people who are otherwise entirely rational — that they are in a duplicate setting. Although they freely admit that this makes no sense, they are still entirely sure of the falseness of their surroundings. Occasionally it spreads to duplicate events as well as settings – one woman believed that her dead husband was in the hospital with her, and another believed that a mugger who had given her the brain injury had actually mugged her on two separate occasions – but most of the time the syndrome is confined to the idea that the patient is living in a set.

Doctors are divided as to what exactly causes this. Some say that it is a simple physical phenomenon. Others say it is the patient's attempt to hide from the fact that their brain is injured. Many of these cases come with visual and spatial disorientation. If the patient feels disoriented, but doesn't know why, they make themselves think that it has something to do with the outside world. That's less scary than believing that there's something vital, but unspecific, wrong with the inside of their head.

There are also parts of the brain that are in charge of generating feelings of familiarity within certain contexts. If those parts are not functioning, the patient has the feeling that they're seeing things that are new, even though they remember seeing them before. The combination makes patients believe that they're in a duplicate setting. Anything to keep them from thinking that their own mind might be injured. Fortunately, this kind of injury seems to heal with time. As patients come to feel that places are familiar, and overcome their disorientation, they once again believe that the world is their own, and not a duplicate.